1. Field of the Invention
This invention relates to melt polymerization processes for producing anisotropic melt-phase forming polymers wherein polymerization temperatures are decreased and/or polymerization rates increased by utilizing a catalyst system, the components of which are more effective when used together than alone. This invention further relates to a processes for producing an anisotropic melt-phase forming polymer consisting essentially of recurring units derived from p-hydroxycarboxylic acid, 6-hydroxy-2-naphthoic acid, at least one aromatic diacid, and at least one aromatic diol, at least a portion of which is resorcinol, wherein said polymer is melt polymerized using a potassium catalyst in combination with a cobalt co-catalyst.
2. Description of the Prior Art
A variety of methods have been disclosed for producing anisotropic melt-phase forming polymers from aromatic hydroxycarboxylic acid, aromatic diol and aromatic diacid reactants, including for example, solution, emulsion and melt polymerizations. Commercially, melt polymerizations offer the advantages of simplicity and lower cost, compared to many solution and emulsion polymerizations. Melt polymerization reactions typically employ a catalyst to promote polycondensation of the reactant materials.
In U.S. Pat. No. 5,616,680, describing the production of aromatic melt-forming polymers having repeating units derived from (a) aromatic hydroxycarboxylic acid, (b) aromatic diol and/or aromatic hydroxyamine and (c) aromatic dicarboxylic acid, polycondensation catalysts are disclosed as including dialkyl tin oxide, diaryl tin oxide, titanium dioxide, alkoxy titanium silicates, titanium alkoxides, alkali and alkaline earth metal slats of carboxylic acids, gaseous acid catalysts and the like. Polycondensation catalysts disclosed in U.S. Pat. No. 4,912,193, describing the production of thermotropic wholly aromatic polyesters containing condensed residues of p-hydroxybenzoic acid, 4,4'-dihydroxydiphenyl isophthalic acid and terephthalic acid, include Lewis acids and hydrohalic acid; oxides, hydrides, hydroxides, halides, alcoholates, phenolates and salts of inorganic or organic acids, complex salts or mixed salts of alkaline earth metals such as magnesium or calcium; of sub-group elements such as vanadium, titanium, manganese, cobalt, nickel, zinc, lanthanum, cerium or zirconium or of elements from other groups of the periodic system, such as germanium, tin, lead and antimony, or the alkali metals or alkaline earth metals as such, in particular sodium; also sodium hydroxide, lithium acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate, cobalt acetate, zinc acetate, calcium benzoate, magnesium acetylacetonate, zinc acetylacetonate, vanadyl-C.sub.1 to C.sub.8 -alkoxides, titatium alkoxides such as titanium tetrabutylate, titanium tetrapropylate, alkoxytitanium silicates, zirconium butylate, zirconium propylate, titanium tetraphenolate, sodium phenolate, germanium dioxide, antimony trioxide, dialkyl and diaryl tin oxide, dibutyl tin diacetate and dibutyl dimethoxy tin. U.S. Pat. No. 5,015,723 discloses processes for producing aromatic polyesters, including aromatic polyesters obtained from an aromatic dicarboxylic acid, an aromatic diphenol and an aromatic oxycarboxylic acid wherein compounds of Ge, Sn, Ti, Sb, Co, Mn, and the like are identified as polycondensation catalysts. Polycondensing aromatic dicarboxylic acids, dihydroxy phenols and p-hydroxybenzoic acid in the presence of a salt such as aluminum acetate, calcium acetate, calcium sulfate, copper acetate, magnesium acetate, magnesium terephthalate, potassium acetate, potassium chloride, potassium phosphate, sodium acetate, sodium sulfate and potassium bisulfate alkaline earth metal salt or an alkali metal salt to form a prepolymer that is subsequently advanced to a desired degree of polymerization by solid stating techniques is disclosed in U.S. Pat. No. 4,742,149.
The catalyst of choice may differ depending upon whether the polymerization proceeds by direct reaction of the aromatic hydroxycarboxylic acid, aromatic diol and aromatic diacid starting materials, as opposed to reaction of the aromatic diacid and an acetylated form of the aromatic diol and aromatic hydroxycarboxylic acid reactants. Reactant composition is another factor that may affect catalyst selection. U.S. Pat. No. 5,656,714, for example, exemplifies the use of a potassium acetate catalyst in the production of a polyester from terephthalic acid, 6-hydroxy-2-naphthoic acid, p-hydroxybenzoic acid, 4,4'-biphenol, and resorcinol; the hydroxyaromatic acid and diol components being acetylated in situ by reaction with acetic anhydride, whereas, U.S. Pat. No. 4,421,908 exemplifies a direct polymerization process wherein 6-hydroxy-2-naphthoic acid, hydroquinone and terephthalic acid are reacted in the presence of a dibutyl tin diacetate catalyst.
It is generally desirable to conduct melt polymerization reactions in the shortest time and at the lowest temperature practical. Frequently these conditions are in an inverse relationship such that by increasing reaction temperature, reaction time is minimized. Increasing reaction temperature may, however, lead to polymer degradation and the production of undesirable by-products. If reaction temperatures are too low, it may not be possible to attain desired molecular weights in commercially viable reaction times. Optimization of reaction conditions can be particularly difficult in situations where the use of numerous raw materials gives rise to competing reaction kinetics. A melt polymerization process for producing an anisotropic melt-phase forming polymer consisting essentially of recurring units derived from p-hydroxybenzoic acid, 6-hydroxy-2-naphthoic acid, an aromatic diol, at least a portion of which is resorcinol, and at least one aromatic dicarboxylic acid utilizing a catalyst system that results in increased reaction rates and/or reduced reaction temperatures is desired.
It is an object of this invention to provide such a process. It is a further object of this invention to produce an anisotropic melt-phase forming polymer consisting essentially of recurring units derived from 6-hydroxy-2-naphthoic acid, p-hydroxybenzoic acid, terephthalic acid, resorcinol and 4,4'-biphenol using a catalyst system that results in increased reaction rates and/or reduced reaction temperatures. These and other aspects of this invention are described in greater detail in the description and examples that follow.